Conventionally, cathode ray tubes mainly have been used as image display apparatuses for color televisions, personal computers and the like. However, in recent years, image display apparatuses have been required to be miniaturized and made lighter and thinner. In order to satisfy these demands, various types of thin image display apparatuses have been developed and commercialized.
Under these circumstances, various types of thin image display apparatuses have been researched and developed recently. In particular, liquid crystal displays and plasma displays have been developed actively. The liquid crystal displays have been applied to various types of products such as portable computers, portable televisions, video cameras, car-navigation systems and the like. Plasma displays have been used for products such as large-scale displays, for example, 20-inch-displays or 40-inch-displays.
However, there are several problems for the liquid crystal displays and the plasma displays. For instance, a liquid crystal display has a narrow visual angle and a slow response. Regarding a plasma display, only high brightness is obtainable and the consumed electricity is large. Then, an image display apparatus (hereinafter referred to as "a field emission image display apparatus" or "an image display apparatus") to which field emission, that is, a phenomenon in which electrons are emitted in a vacuum at room temperature, is applied, has attracted considerable attention. The field emission image display apparatus is of a spontaneous luminescent type, and therefore it is possible to obtain a wide visual angle and high brightness. Further, its basic principle (to illuminate a fluorescent substance with electron beams) is the same as that of a conventional cathode ray tube, and therefore, images with natural color and high reproduction can be displayed.
Published Unexamined Japanese Patent Application (Tokkai-Hei) 3-149728 discloses an example of such a field emission image display apparatus. The field emission image display apparatus that is driven under a vacuum condition from 1.times.10.sup.-7 to 1.times.10.sup.-8 torr should be produced generally by vacuum-sealing the inner part. Therefore, the thin field emission image display apparatus should have a structure to be resistant to the atmospheric pressure. For the purpose of obtaining a structure resistant to the atmospheric pressure, Tokkai Hei 3-149728 discloses a technique for providing a supporting member to the inner part of a field emission image display apparatus.
FIG. 12 is a schematic cross-sectional view showing a field emission image display apparatus according to a conventional technique. The field emission image display apparatus shown in FIG. 12 comprises an electron emission source 101 comprising an insulating substrate 101a provided thereon with plural electron sources 101b, a fluorescent layer 102 formed on the inner surface of the image display apparatus's panel to face the electron emission source 101, and supporting members 103 provided between the electron emission source 101 and fluorescent layer 102. The supporting members 103 are provided uniformly on the electron emission source 101 in order to prevent damage caused by outside pressure applied to the panel in the area between the electron emission source 101 and the fluorescent layer 102.
FIG. 13 is a schematic cross-sectional view showing another conventional field emission image display apparatus. Like the field emission image display apparatus shown in FIG. 12, this field emission image display apparatus comprises an electron emission source 201 comprising an insulating substrate 201a provided thereon with plural electron sources 201b, a fluorescent layer 202 and supporting members 203 formed between the electron emission source 201 and the fluorescent layer 202. The supporting members 203 are uniformly formed on the electron emission source 201 in order to prevent damage caused by the outside pressure applied to the panel in the area between the electron emission source 201 and the fluorescent layer 202. This image display apparatus is distinguishable from the former one in that the supporting members 203 composing the field emission image display apparatus in FIG. 13 are negatively charged while the supporting members 103 composing the field emission image display apparatus in FIG. 12 are positively charged.
An image display apparatus shown in FIG. 12 or 13 comprises the supporting members (103, 203) between the electron emission source (101, 201) and the fluorescent layer (102, 202), so that the field emission image display apparatus has a structure resistant to the atmospheric pressure. Electron beams (104, 204) are emitted from the electron sources (101b, 201b) formed with equal spacing on the insulating substrate (101a, 201a) and landed on predetermined positions of the fluorescent layer (102, 202), so that various images are displayed on the field emission image display apparatus. Various members required other than the above-identified ones for forming a field emission image display apparatus are omitted in FIGS. 12 and 13.
However, in the conventional field emission display apparatus in FIG. 12, the electron beams 104 emitted at an equal spacing will bend toward the supporting members 103 since the supporting members 103 are positively charged, and thus, the final landing positions of the electron beams 104 will not be spaced equally on the fluorescent layer 102. Similarly in the field emission image display apparatus shown in FIG. 13, the electron beams 204 emitted at an equal spacing will bend away from the supporting members 203 since the supporting members 203 are negatively charged, and thus, the final landing positions of the electron beams 204 will not be spaced equally on the fluorescent layer 202. As a result, the electron beams (104, 204) are deviated from the landing positions on the fluorescent layers (102, 202), and good images are difficult to obtain.
The supporting members (103, 203) composing the field emission image display apparatus have a predetermined thickness at the positions contacting with the fluorescent layer (102, 202). When this thickness exceeds a limit, it will be recognized as a horizontal line by someone watching the displayed images and the quality of the display images will be greatly lowered.
Furthermore in the conventional technique, plural supporting members (103, 203) are provided between the electron emission source (101, 201) and the fluorescent layer (102, 202). If the supporting members (103, 203) have different lengths, outside pressure will be applied only to the longer supporting members contacting with the fluorescent layer (102, 202), which may result in distortion or damage for the image display apparatuses.